Fiber Reinforced Polymer (FRP) Bridge Decks
Fiber reinforced polymer (FRP) composite bridge decks are pre-engineered and prefabricated in a manufacturer’s shop, and then assembled and installed at the bridge site. A wearing surface or overlay is typically installed after all the FRP deck panels are installed. FRP deck panels are engineered materials with their strength dependent on several factors, including fiber type, volume percent of fibers, fiber orientation, resin type, manufacturing methods, and bonding materials used in the final assembly. FRP bridge decks are typically fabricated with vinyl ester or polyester resin reinforced with E-glass fibers (22).
FRP deck panels weigh much less than a comparable reinforced concrete bridge deck. A typical FRP deck with a wearing surface or overlay may weigh between 25 to 70 pounds per square foot of deck, as compared to a conventional 9.5 inch thick reinforced concrete deck that weighs 120 pounds per square foot of deck. Figure 17 shows the installation of an FRP deck panel using a forklift type vehicle. FRP deck panels are also more resistant to deicing salts and other materials that can result in degradation of a conventional reinforced concrete deck. FRP deck panels can be installed faster than a conventional reinforced deck, making FRP deck panels advantageous in rehabilitation projects where bridge closure time is of concern.
However, FRP deck panels have a higher initial cost as compared to conventional reinforced concrete decks. The design of FRP decks is also proprietary and there are currently no standard manufacturing processes. FRP decks are also subject to degradation resulting from the overexposure to ultraviolet radiation, and there is reluctance to use FRP bridge decks due to the lack of long term performance data. Since FRP decks are prefabricated, they have little tolerance for existing conditions when used in bridge rehabilitation projects, and can not be adjusted as easily as a conventional reinforced concrete deck.
Currently, there are several active research projects that may further the use of FRP bridge decks. The Federal Highway Administration (FHWA) has contracted studies that may evolve into AASHTO guidelines for the design and construction of FRP bridge decks, as well as material standards (22).
Per an advisory published by the FHWA (22), a designer may specify an FRP deck system if it appears on the purchasing agency’s (bridge owner) approved list of materials or meets nationally accepted testing standards. Design calculations certified by a Professional Engineer, an installation procedure, and working drawings are required to be submitted by the FRP deck supplier for review by the bridge owner. Wearing surface materials are also to be selected from an approved list if not listed specifically as part of the preapproved deck system. Suppliers are responsible for the certification of the finished product as well as quality control during the manufacturing process. Though not mandatory, the designer may want to consider specifying that FRP deck is load tested prior to placing the bridge in service. This will serve to verify theoretical finite element models of FRP bridge decks and design computations.
For more information regarding the advantages and disadvantages of FRP decks, construction methods, considerations for the use of FRP decks, and general design criteria, the reader should refer to the FHWA advisory titled Current Practices in FRP Composite Technology FRP Bridge Decks and Superstructures (22).